1. Field of the Invention
The invention relates to a biosensor, and in particular to a ruthenium oxide electrode and fabrication method thereof.
2. Description of the Related Art
Ruthenium (Ru), a noble metal, as an oxide possesses super-high capacitance due to double layer mechanism and pseudo-capacitance resulting from redox with solution on the surface of ruthenium oxide. The latter provides a tenfold increase in charge storage capacity. Ruthenium dioxide is similar to metal in its low resistivity (less to 10−4 ohm·cm) and high surface area (about 800-1000 m2/g). Other advantages include high conductance, multi-redox-active pairs [Ru(II)-Ru(III)-Ru(IV)-Ru(V)-Ru(VI)-Ru(VII)], superior adhesion with enzymes and compounds, reversibility in electrochemistry, stability in acid solution, and application in pH-measuring membrane material.
In 2002, Erlenkotter et al. (A. Erlenkotter, M. Kottbus, G. C. Chemnitius, “Flexible amperometric transducers for biosensors based on a screen printed three electrode system”, Journal of Electroanalytical Chemistry, vol. 481, pp. 82-94, 2000.) presented the kinetics parameters of electrodes with changed scan rate. The active surface area of the Pt working electrode was determined using electrochemical studies. Cyclic voltammograms of the ferricyanide/ferrocyamide couple showed that the reaction was quasi-reversible at these electrodes.
A number of patents related to ruthenium oxide membrane and fabrication methods are summarized as follows.
U.S. Pat. No. 6,383,363, inventors: Jow; T. Richard (Chatham, N.J.); Zheng; Jian-Ping (Eatontown, N.J.), patent title: “Proton inserted ruthenium oxide electrode material for electrochemical capacitors”, Pub. Date: May 7, 2002, abstract: A high energy density electrochemical capacitors with electrodes is formed from proton inserted ruthenium oxides (e.g. HRuO2.xH2O or HRuO2). The electrode material is formed by reducing ruthenium oxides (e.g. RuO2.xH2O or RuO2) using electrochemical method or chemical reaction between ruthenium oxides with acetone or methanol. Electrochemical capacitors with electrodes formed of proton inserted ruthenium oxides possess higher energy density, lower resistance, broader operating temperature range, and longer lifetime than that with electrodes comprised ruthenium oxides.
U.S. Pat. No. 6,239,460, inventors: Kuroiwa; Takeharu (Tokyo, JP); Horikawa; Tsuyoshi (Tokyo, JP); Makita; Tetsuro (Tokyo, JP); Mikarni; Noboru (Tokyo, JP); Shibano; Teruo (Tokyo, JP), patent title: “Semiconductor device which includes a capacitor having a lower electrode formed of iridium or ruthenium”, Pub. Date: May 29, 2001, abstract: A semiconductor device such as DRAM including a capacitor, wherein a lower electrode of the capacitor is a metal electrode, the metal electrode being mainly composed of ruthenium or iridium, and being connected directly to a capacitor dielectric film through no oxide layer of materials of the metal electrode formed on the surface of the metal electrode. The lower electrode made of iridium or ruthenium can easily be processed as compared with the conventional case where platinum is employed to form the electrode and also can not be oxidized when the capacitor dielectric film is formed, thus reduction in the capacitance can be prevented.
U.S. Pat. No. 5,619,393, inventors: Summerfelt; Scott R. (Dallas, Tex.); Beratan; Howard R. (Richardson, Tex.); Gnade; Bruce E. (Dallas, Tex.), patent title: “High-dielectric-constant material electrodes comprising thin ruthenium dioxide layers”, Pub. Date: Apr. 8, 1997, abstract: A preferred embodiment of this invention comprises a thin unreactive film (e.g. ruthenium dioxide) contacting a high-dielectric-constant material (e.g. barium strontium titanate) to an electrode. The thin unreactive film provides a stable conductive interface between the high-dielectric-constant material layer and the electrode base (e.g palladium). As opposed to a standard thin-film layer, the thin unreactive film is generally less than 50 nm thick, preferably less than 35 μm thick, more preferably between 5 nm and 25 nm thick, and most preferably between 10=m and 20 nm thick. A thin unreactive film benefits from the advantages of the materials used while avoiding or minimizing many of the disadvantages. A thin unreactive film is substantially less costly than a standard thin-film layer since much less material is used while not significantly affecting the surface area of the electrode in contact with the HDC material. These structures may also be used for multilayer capacitors and other thin-film ferroelectric devices such as pyroelectric materials, non-volatile memories, thin film piezoelectric and thin film electro-optic oxides.
U.S. Pat. No. 5,358,889, inventors: Emesh; Ismail T. (Cumberland, Calif.); McDonald; David R. (Ottawa, Calif.), patent title: “Formation of ruthenium oxide for integrated circuits”, Pub. Date: Oct. 25, 1994, abstract: A method is provided for forming a conductive layer of ruthenium oxide layer RuO2. The RuO2 layer is formed from a coating of a precursor solution comprising a ruthenium (III) nitrosyl salt, subsequent heat treatment, and annealing at low temperature. The resulting layer of a tetragonal phase of crystalline ruthenium oxide is suitable to receive formation thereon of a perovskite structure ferroelectric material for applications in ferroelectric non-volatile memory cells. The chloride free process is compatible with processing for submicron device structures for bipolar, CMOS or bipolar CMOS integrated circuits.